Digital type vehicle brake control system

ABSTRACT

A digital type vehicle brake control system which serves to interrupt the communication of the brake fluid pressure between a master cylinder and the wheel cylinders of the vehicle and to vary the fluid volumes in the system, in which a digital type control is applied throughout the brake control processes from detection of the wheel rotational conditions up to control of the brake fluid pressure.

United States Patent [191 Hida et al.

1 DIGITAL TYPE VEHICLE BRAKE CONTROL SYSTEM [75] Inventors: TakashiHida; Katsuki Takayama;

Kazutaka Kuwana; Junichiro Ooya, all of Kariya, Japan [73] Assignee:Aisin Seiki Kabushiki Kaisha,

Aichi-ken, Japan 22 Filed: Mar. 16, 1972 21 Appl. No.: 235,212

[30] Foreign Application Priority Data Mar. 20, 1971 Japan 46-16008 Mar.20, 1971 Japan 46-16009 [52] US. Cl 303/21 EB, 188/181 C, 235/1502,303/20, 303/21 P, 303/21 CO [51] Int. Cl B60t 8/08 [58] Field of Search188/181 C; 235/1502;

BLOCK I1 Apr. 23, 1974 [5 6] References Cited UNITED STATES PATENTS3,608,978 9/1971 Neisch 303/21 EB 3,620,577 11/1971 Neisch et al....'303/21 EB 3,589,776 6/1971 Wehde 1 303/21 CF UX 3,586,385 6/1971 Floruseta. 303/21 EB UX Primary ExaminerDuane A. Reger AssistantExaminer-Stephen G. Kunin Attorney, Agent, or Firm-Holman & Stern [5 7]ABSTRACT A digital type vehicle brake control system which serves tointerrupt the communication of the brake fluid pressure between a mastercylinder and the wheel cylinders of the vehicle and to vary the fluidvolumes in the system, in which a digital type control is appliedthroughout the brake control processes from detection of the wheelrotational conditions up to control of the brake fluid pressure.

6 Claims, 16 Drawing Figures l-ATENTEDAPR2319M 3806205 sum 02 or 14 FIG.2

I9. 20 TO WHEEL 49 39 CYLINDERS TO ENGINE INTAKE 36 3O 32 742 4|MANIHOLD TO MASTER CYLINDER SHEET GU UP 14 FIG. 3(b) PATENTEDAPII 23I974 T Q. 6-: R S

SHEET US IIF 14 F I G. 4

Q 6 s R Q 6 T I R S L L (H) (H) TRIGGER TERMINAL H H I TERMINAL H H 0TERMINAL H I H n n RESET TERMI AL Q Q sET TERMINAL IN cAsE No WIRING ISMAD o TERMINALS 8 AND R, THEY ARE AT THEH LEvEL Qn: WHEN THE LEVELOFTI-IE RIBGER TERMINAL IS CHANGED mm H TO L. THE coNDITIoN IMMEDIATELYBEFORE THIs CHANGE IS INvERTED F I G. 5

Q 6 In In+ I In BIT TIME T S BEFoRE D D Q Q CLOCK PULSE In+I: BIT TIME LH AFTER H H L CLOCK PULSE WHILE CLOCK PU SE IS AT THE H LEVEL.INFORMATION GIVEN TO INPUT IS TRANSFERRED TO OUTPUT Q AS IT IS WHENCLOCK PULSE COMES TO BEAT L" LEVEL, OUTPUT Q REMAINS UNCHANGED UNTILCLOCK PULSE COMES TO BE H"LEVEL A DIRECT SETTING .CAN BE MADE IN c sENoAT H LEVEL PATENTEBAPR r914 saw 05 0F 14 FIG.6

OUTPUT INPUT INPUT OUTPUT D O B A O I 2 3 4 5 6 7 8 9 D C B A O I 2 3 45 6 7 8 9 L L L L L H H H H H H H H H H L L, L H H H H H H H H L H L L LH H L H H H H H H H H H L L H H H H H H H H H H L L L H L H H L H H H HH H H H L H L H H H H H H H H H H L L H H H H H L H H H H H H H L H H HH H H H H H H H H L H L L H H H H L H H H H H H H L L H H H H H H H H HH L H L H H H H H H L H H H H H H L H H H H H H H H H H H L H H L H H HH H H L H H H H H H L H H H H H H H H H H L H H H H H H H H H H L H H HH H H H H H H H H H H H FIG? 2 3 4 5 6 7 8 9 IO II [2 l3 l4 l5 COUNT ODLLLLLLLLHHHHHUHHH PATENTEDAPR a a new SHEET 09 HF 14 IIIIIIII IIIIIIIINmEEDSUa a 5:8 IIIIIIIIIIIIIIII mmmfizaohauumsu IIIIIIIIIIIIIIIINmEEdSmQmSEO IIIIIIIIjjjj -mz38h5 55o IIIIjj 11.2 3 3 1:11 3 3 5 mEZDSUa0 :8 IIjIIjIIjIIjIIjIIj5 1858% @5150 51455 141 2414 1 5455 mz=8% :8 1 IvQ I I 8 mm I 1 I mm hw om E 1 E z. I 1 I I vw 8 mm B :8 .258 Q iiii -9mm mm m 8 IIIII :2 2 lllll w E 85: lllll wiwmvmfo A vm 0 11:11:11 11111111111111 QE SEE N 5% IIIIIIIIIIQIIIIIIIIIIIII a $8808 m 5%IIIIIIIIIIIIQIIIIIIIIIII m EQSMQ a m 52 IIIIIIIIIIII IQIIIIIIIII m ESE a5%:

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jjjjIIIIIIII jjjj ZE E SHEET 10 [1F 14 mm I I I I I- 5500 mm llll II N 1I I miwmwmw o PATENTEDAPR 23 1974 PATENTEUAPHBIBM Q T 3.806205 SHEET 13of 1 1 FIG. II (b) H OUTPUT OF NAND ELEMENT M34 L OUTPUT OF NAND ELEMENTM33 OUTPUT OF NAND' ELEMENT M30 H OUTPUT OF NAND ELEMENT M3:

H OUTPUT 0F NAND ELEMENT M32 PATENTEBAPR 23 1974 SHEET 1n OF 14 OUTPUT(3 OF FLIPFLOP F19 IS ELEMENT N2 I OUTPUT OF NAND H ELEMENT M39 OUTPUTOF NAND ELEMENT M40 Y HH GHHL 5HLH 4 L 3LHH ZLHL I LH OLLL QQQ TT WUUPPP T TT W m 0 00 C mam FFF DIGITAL TYPE VEHICLE BRAKE CONTROL SYSTEMBACKGROUND OF THE INVENTION If a conventional vehicle brake systemexerts an emergency brake force, when the coefficient of frictionbetween a road surface and the wheel tire of the vehicle is small, andwhile an engine driving force is applied to the wheels the drivingwheels are frequently locked because the wheel speed is only restoredslowly even if the brake liquid pressure is reduced.

In additional, where the brake liquid pressure is controlled in thistype of conventional brake control systerns, the pressure-reducing rateand pressure-restoring rate with respect to the brake liquid pressureare deter mined in accordance with a predetermined pattern. Therefore,the brake control system cannot sufficiently follow the speedvariation'of the wheel being braked, as a result of which the speedvariation of the wheel being braked increases, the braking distance alsoincreases, and the stability and steerage of the vehicle is lowered.

SUMMARY OF THE INVENTION braking is secured by preventing the lockingphenomena which occurs during application of an emergency brake, so thatoptimum brake force can be obtained under any condition.

A second object of the present invention is to provide 7 a digital typevehicle brake control system, in which by application of digital typemeans the rate of brake pressure application is varied and the variationof the wheel control rate is made to be small when compared with aconventional anti-skid brake control system, whereby the vehicletravelling stability is improved and the braking distance is reduced.

A third object of the present invention is to, provide a digital typevehicle brake control system, in which a circuit for controlling a brakeliquid pressure does not include an analog circuit, and therefore errorscaused by variation on the' characteristics of elements which form thebrake control system and by frequency characteristics thereof can bereduced.

A fourth object of the present invention is to provide a digital typevehicle brake control system, in which a special temperaturecompensation circuit is not necessary for counteractingtemperature-drift which is caused by the temperature dependability ofelements constituting the brake control system, and even though thecharacteristics of the elements used in the brake control system varywith elapse of time the capability of a computer is not affected by thevariation on the characteristics.

A fifth object of the present invention is to provide a digital typevehicle brake control system, in which tolerances for the precisions ofelements which form the brake control system can'be relatively large,and a digital circuit which does not employ an inductance or a capacitorhaving a large capacity is used thereby to i be suitable for a largescale production as an integrated circuit.

A sixth object of the present invention is to provide a digital typevehicle brake control system, in which the rate of controlling the brakeliquid pressure of a vehicle corresponds to the variation of the speedof the wheel being braked and the pressure-reducing rate andpressure-restoring rate are variably controlled in double steps, as aresult of which the variation on the wheel speed is considerably smalland the braking distance of the vehicle is much shorter than that in theconventional brake control system.

The foregoing objects and other objects as well as the characteristicsfeatures of the present invention will become more apparent from thefollowing detailed description and the appended claims when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE INVENTION In the accompanying drawings:

FIG. 1 shows an embodiment of the vehicle brake system according to thepresent invention;

FIG. 2 is a longitudinally sectioned view of an actuator employed in thebrake control system according to the present invention;

FIGS. 3a -3b illustrate an embodiment of the electrical circuit employedin the present invention;

FIGS. 4 and 5 exhibit the truth tables of flipflop circuits;

a FIG. 6 is the truthtable of a decoder;

FIG. 7 is the truth table of a counter; and

FIGS. 8a, 8b, 9a, 9b, 10, 11a, 11b, and 12 explain the operationalconditions of various elements used in the present invention.

In connectionwith the accompanying drawings, FIGS. 3, 8, 9 and 11 aredivided into twoparts (a) and (b), respectively, because each of thefigures are too large to be put on one sheet.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION Withreference now to FIG. 1, namely, a systematic diagram, there is shown anembodiment of the present invention, which comprises a well-known tandemmaster cylinder 11 which is adapted to produce a hydraulic oil pressureby depressing a brake pedal; pipes 17 and 18 which communicate betweenthe master cylinder 11 and wheel cylinderslS, 15a, 16 and 16a providedin front and rear wheels 13, 13a, 14 and 14a, respectively; actuators 19and 20 provided in the middle parts of the pipes 17 and 18,respectively, said actuators being adapted to control the oil pressurefrom the master cylinder 11 with the aid of electromagnetic solenoids21, 22, 23 and 24, and to exert thus controlled oil pressure on thewheel cylinders 15, 15a, 16 and 16a, respectively; sensors 25, 25a, 26and 26a provided on the front and rear wheels 13, 13a, 14 and 14arespectively, said sensors being adapted to produce electrical signalsin the form of sine waves or pulse waves corresponding to therevolutions of the wheels; and a controller 27 which receives theoutputs of the sensors 25, 25a, 26 and 26a thereby to apply electricalsignals to the actuators l9 and 20 as described later. The actuators 19and 20. serve to control the braking pressure of the master cylinder 11in accordance with the electrical signals produced by the controller 27and to exert the thus controlled braking pressure on the wheel cylinders15, 15a, 16 and 16a.

Referring now to FIG. 2, there is exhibited an embodiment of theactuators 19 and 20, which comprises a body 28 and a fluid pressure typedifferential device 29. Passages 31 and 32 are formed in the cylinder 30of the body 28, and the passages 31 and 32 communicate with the mastercylinder 11 and the wheel cylinders 15, 15a, 16 and 16a, respectively.The passage 31 communicates with the other passage 32 through a chamber33. a passage 34 and a passage 35. The body 28 is further provided witha plunger 36 which is slidably fitted in the cylinder 30 in its axialdirection. The plunger 36 has a protruded part 37 on its right end, andthe diameter of the protruded part 37 is smaller than that of theplunger 36, while the left end of the plunger 36 is connected to adiaphragm 40 whose peripheral portion is inserted between the joiningparts of housing 38 and 39. A ball valve 42 is held in contact with theprotruded part 37 of the plunger 36 by means of a spring 41 which issupported in the chamber 33. The cylinder 30 forms a valve seat 43 forthe ball valve, 42. The diaphragm 40 is provided with a spring retainer44, and a restoring spring 45 is loaded between the spring retainer 44and the housing 38.

A passage 46 is also formed in the housing 38. The passage 46communicates with an engine intake manifold (not shown) through a pipe47 and also with a chamber 49. The chamber 49 is formed by the housings38 and 39, and the cylinder 30, and is divided into two parts by meansof the diaphragm 40 thereby providing an additional chamber 49 in it.The chamber 49 thus provided communicates with a passage 53 through apipe 50, the passage 53 being provided in the housing 52 of anelectromagnetic switching valve 51.

The housing 52 of the electromagnetic switching valve 51 is furtherprovided with passages 54 and 55 which in turn communicate respectivelythrough pipes 56 and 57 with a passage 60 formed in the housing 59 of anelectromagnetic air-switching valve 58. A plunger 61 is slidably fittedin the electromagnetic switching valve 51, and one of the ends of theplunger 61 is formed to be a valve 62. Under normal conditions, thevalve 62 is abutted against an annular valve seat 65 provided on thehousing 52, by means of a spring 64.

loaded between the other end of the plunger 61 and a plug 63. Under thiscondition, the communication between the pipes 50 and 56 is interruptedor cut off, whereas the communication between the pipes 50 and 57 isestablished.

The passage cross-sectional area of the pipe 57 is smaller than that ofthe pipe 56. The previously mentioned electromagnetic solenoid 22 (24)is wound on the peripheral part of the plunger 61. When theelectromagnetic solenoid 22 (24) is energized, the plunger 61 isattracted toward the left (in FIG. 2) against the electric force of thespring 64, while the valve 62 is moved off the annular valve seat 65 andis abutted against the other valve seat 67 provided in the valve 51.

The arrangement of the electromagnetic airswitching valve 58 is almostsimilar to that of the electromagnetic switching valve 51. That is, avalve 69 is provided on one of the ends of a plunger 68 which isslidably fitted in the electromagnetic air-switching valve 58. Undernormal conditions, the valve 69 is abutted against an annular valve seat72 formed in the housing 59, by the elastic force of a spring 71 whichis loaded between the plunger 68 and a plug 70. The previously describedelectromagnetic solenoid 21 (23) is wound on the peripheral portion ofthe plunger 68. The air-switching valve 58 is further provided with anair filter 74 which opens to the atmosphere through passages 75, andunder the conditions shown in FIG. 2 the communication between the pipes56 and 57 and the atmosphere is cut off. When the electromagneticsolenoid 21 (23) is energized, the plunger 68 is attracted toward theleft (in FIG. 2) against the elastic force of a spring 71 and at thesame time the valve 69 is moved off the valve seat 72 and is abuttedagainst the other valve seat 76 provided in the housing 59. A passage 77is formed in the housing 59 so as to communicate with the intakemanifold.

The operations of the actuators 19 and 20 are as follows:

Since a pipe 78 is connected to the engine intake manifold(not shown),the pipe 78 remains negative in pressure at all times, and the passagesopen to the atmosphere. When no electric current flows through theelectromagnetic solenoid 21 (23), or the solenoid 21 (23) is notexcited, the plunger 68 cuts off the communication between the passages75 and 60 and at the same time establishes the communication between thepipe 78 and the passage 60. Therefore, the passage 60 is brought to benegative in pressure, as a result of which the chamber 49 of the fluidpressure type differential device 29. is also made to be negative inpressure through the electromagnetic switching valve 51. On the otherhand, the chamber 48 also communicates with the engine intake manifold,and the pressure in the chamber 49 is always negative. Therefore, thediaphragm 40 serves to push the ball valve 42 toward the right (in FIG.2) with the aid of the plunger 36 and to hold the ball valve 42 againstthe elastic force of the spring 41 as shown in FIG. 2, whereby the oilpressure of the master cylinder is made to be equal to those of thewheel cylinders.

Now, when an electric current is applied to fiow through theelectromagnetic solenoid 21 (23) thereby to produce a magnetic forcetherefrom, the plunger 68 is moved ,leftwardly against the elastic forceof the spring 71 by the thus produced magnetic force, as a result ofwhich the communication between the pipe 78 and the passage 60 is cutoff and the communication between the atmosphere passages'75 and thepassage 60 is set up. This means that the atmospheric pressure isapplied to the chamber 49 through the filter 74, passage 60,electromagnetic switching valve 51 and pipe 50 thereby to change thenegative pressure of the chamber 49 to be equal to the atmosphericpressure. As a result, the diaphragm 40 is displaced against the elasticforce of the spring 45 in such a direction that the ball valve 42interrupts the communication between the master cylinder 11 and thewheel cylinders 15, 15a, 16 and 16a. The plunger 36 maintains itsdisplacement even after the communication between the master cylinder 11and the wheel cylinders 15, 15a, 16 and 16a has been cut off, so thatthe chamber 35 increases in volume. As a result of which the oilpressures of the wheel cylinders 15, 15a, 16 and 16a are reduced.

Under this condition, if an electric current to the electromagneticsolenoid 21 (23) is cut off, the plunger 68 is returned back to theposition shown in F IG. 2 by the elastic force of the spring 71 therebyto establish the communication between the pipe 78 and the passage 60and to cut off the communication between the atmospheric passages 75 andthe passage 60. Accordingly, the pressure of the chamber 49 is changedfrom the atmospheric pressure to the negative pressure, and

- the diaphragm 40 is moved by the elastic force of the spring 45 insuch a direction that the volume of the chamber 35 decreases, and afterthe reduced oil pressure of the wheel cylinders has been restored backits original pressure, the ball valve 42 is relieved against the elasticforce of the spring 41 thereby to make equal both oil pressures of thewheel cylinders and master cylinder. In other words, the electromagneticairswitching valve 58 reduces the oil pressure of the wheel cylindersupon application of the electric current to the electromagnetic solenoid21 (23), and restores the oil pressure of the wheel cylinders back tothat of the master cylinder when the flow of the electric current in theelectromagnetic solenoid 2 1 (23) is cut off.

When no electric current flows through the electromagnetic solenoid 22(24) of the electromagnetic switching valve 51, the communicationbetween the pipes 56 and 50 is cut off while the pipes 57 and 50 arecommunicated with each other. As stated before, the inside diameter ofthe pipe 57 is smaller than that of the pipe 56, as a result of which arate at which the pressure of the chamber 49 is varied from the negativepressure to the atmospheric pressure or vice versa becomes slower thanin the case when the pressure in the chamber 49 is made to be variablethrough the pipe 56. Therefore, the moving rate of the diaphragm 40 andplunger 36 is caused to be slower, and the pressurereducing rate andpressure-restoring rate of the wheel cylinder oil pressure are caused tobe slow.

When the electric current flows through the electromagnetic solenoid 22(24) of the electromagnetic switching valve 51 the plunger 61 is movedleftwardly against the elastic force of the spring 64, as a result ofwhich the communication between the pipes 50 and 57 is cut off while thepipes 50 and '56 are communicated with each other. Since the insidediameter of the pipe 56 is much larger than that of pipe 57, a rate atwhich the pressure of the chamber 49 is varied from the negativepressure to the atmospheric pressure or vice versa is quicker than inthe above-mentioned case where the rate is slower, as a result of whichthe moving rate of the diaphragm 40 and plunger 36 is also caused to bequicker and the pressure-reducing rate and pressurerestoring rate of thewheel cylinders are made to be quicker. In other words, theelectromagnetic switching valve 51 serves to make quick thepressure-reducing rate and pressure-restoring rate of the wheelcylinders oil pressure upon application of an electric current to theelectromagnetic solenoid 22 (24), and serves to make said rates slowwhen the application of the electric current to the solenoid 22(24) isceased.

Shown in FIG. 3 is an embodiment of the controller described withreference to FIG. 1, which comprises six blocks, block I through blockVI. Blocks 1 to III mainly serve to control the actuator 19 provided forthe front wheels, whereas blocks IV to VI mainly serves to control theactuator provided for the rear wheels. The circuit compositions ofblocks I to III are similar to those of blocks IV to VI, and therefore adetailed description of the later circuits will not be given.

Amplifiers A, and A, may be, of course, any of the operation amplifier,IC amplifier and transistor circuit amplifier. NAND elements M, throughM have amplification and NAND functions that is, only when all theinputs of the NAND element are at H levels, its output will be at an Llevel, and when any of the inputs is at the L" level, its output will atthe H level. In this connection, the H level means a high logicpotential while the L" level means a low logic potential.

NOR elements N, and N have amplification and NOR functions that is, onlywhen all the inputs of the NOR element are at an L levels, its outputwill be at an H level, and when any of the inputs is at the H level, itsoutput will be at the L level. Flipflops F, to F are of directconnection type R-S flipflops whose truth table is as shown in FIG. 4.Flipflops F to F are of D flipflops whose truth table is as shown inFIG. 5. A decoder E, is a binary coded decimal decoder, whose truthtable is as shown in FIG. 6. Counters B, and B are 4-bit binary counterswhose truth table is as shown in FIG. 7.

The circuit compositions of all the blocks-are as follows. First of all,blocks I and IV will be described.

In blocks I and IV; the output of the sensor 25 (for the right frontwheel) is connected to the input of the amplifier A, in block I, and theoutput of the sensor 26 (for the right rear wheel) is connected to theinput of the amplifier A, in'block IV. In the same way, the output ofthe sensor 25a (for the left front wheel) is connected to the input ofthe amplifier A, in block I, and the output of the sensor 26a (for theleft rear wheel) is connected to the input of the amplifier A in blockIV. The output of the amplifier A, is connected through a resistor R,'to the NAND element M, whose output is connected to the NANDelement Mandto a capacitor C The output of the NAND element M is connected to oneterminal of a capacitor C and through a resistor R to the resistor R,and the input of the NAND element M,. Said resistors R, and R and NANDelements M, and M constitute a wellknown wave form shaping circuit. Theother terminal of the capacitor C, is connected to one terminal of aresistor R one terminal of a resistor R,, and an input of the NANDelement M The other terminal of the resistor R,, is connected to anelectrical source voltage, and the other terminal of the resistor R isgrounded. The capacitor C, and resistor R and R, form a well-knowndifferentiation circuit. The other terminal of the capacitor C isconnected to the terminals of resistors R and R,,, an input of the NANDelement M and an input ofthe NAND element M Said capacitor C andresistors R,, and R,, constitute a well-known differentiationcircuitsThe other terminal of the resistor R is connected to theelectrical source voltage, and the other terminal of the resistor R,,isgrounded.

The output of the amplifier A is connected through a resistor R to theNAND element M and the output of the NAND element M is in turn connectedto the NAND element M, and one terminal of a capacitor C The output ofthe NAND element M, is connected to one terminal of a capacitor C andthrough a resistor R,,, to the NAND element M The resistors R and R,,,,and NAND elements M and M form a well-known waveform shaping circuit.The other terminal of the capacitor C is connected to terminals ofresistors R,, and R,, and to an input of the NAND element M The otherterminal of the resistor R,, :is connected to the electrical sourcevoltage, and the other terminal of the resistor R,, is grounded. Thecapacitor C, and resistors R,, and R,,, in combination form a well-knowndifferentiation circuit.

The other end of the capacitor C,, is connected to terminals ofresistors R,,, and R,,, an input of the NAND element M and an input ofthe NAND element M The other terminal of the resistor R is connected tothe electrical source voltage, and the other terminal of the resistor Ris grounded. The capacitor C and resistors R and R in combination form awell-known differentiation circuit. The output of the NAND element M isconnected to one terminal of a capacitor C and in block II to an inputof the NAND element M20 and an input of the NAND element M The otherterminal of the capacitor C is connected to one terminal of a resistor Rand an input of the NAND element M The other terminal of the resistor Ris grounded. The output of the NAND element M is connected to an inputof the NAND element M The output of the NAND element M is connectedthrough a capacitor C to one terminal of a resistor R and an input ofthe NAND element M The other terminal of the resistor R is grounded. Theoutput of the NAND element M is connected to inputs of the NAND elementsM M M and M respectively. The output of the NAND element M is connectedthrough a capacitor C to one terminal ofa resistor R and an input of theNAND element M and the other terminal of the resistor R is grounded. Theoutput of the NAND element M 'is connected to inputs of the NANDelements M M and M .-The output of the NAND element M is connected to aninput of the NAND element M the output of the NAND element M is in turnconnected to a trigger input of the flipflop F and aninput of the NANDelement M The output of the NAND element M is connected to an input ofthe NAND element M whose output is connected to inputs of the NANDelements M and M The output of the NAND element M is connected to aninput of the NAND element M The abovementioned combinations of the NANDelements M and M capacitor C and resistor R of the NAND elements M and Mcapacitor C and resistor R and of the NAND elements M and M capacitor Cand resistor R form well-known mono-stable multi-vibrator circuits,respectively. In addition, the NAND elements M and M form a well-knownflipflop circuit.

An output Q of the flipflop F, in block I is indicated as FP, an outputQ of the flipflop F, in block IV as RP;

an output of the NAND element M in block I as Fl,

an output of the NAND element M in block IV as RT; an output of the NANDelement M in block I as F0, and an output of the NAND element M in blockIV as R0. The other circuit compositions are completely the same inblocks I and IV.

Now, the circuit compositions of blocks II and V will be described. Awell-known oscillator is formed with capacitors C and C diodes D and Dresistors R and R and NAND elements M and M The operation of theoscillator thus formed is as follows: If it is assumed that an input ofthe NAND element M is made to be at an L level (low level) by turning onan electrical source switch, the output terminal of the NAND element Mwill be at an H level (high level), the input terminal of the NANDelement M will be at the level and the output terminal of the NANDelement M will be at the L level.

The high potential on the input side of the NAND element M is loweredthrough the diode D and resistor R in accordance with a time constantwhich is proportional to the production of the capacitor C and theresistor R When the potential on the input side of the NAND element Mreaches the L" level owing to discharge, the output side of the NANDelement M will be at the H level. A time T, for which the outputpotential of the NAND element M remains at the L level is a half periodof the oscillator. If the output ter minal of the NAND element M is madeto be at the H level, the input terminal of the NAND element M ischanged from L level to H level, and the output terminal of the NANDelement M is changed from H level to L level. In the same way asdescribed with respect to the NAND element M the H level of the inputterminal of the NAND element M is changed to the L level, and its outputterminal is changed from L level to H level due to the level changecaused on the input terminal. A time T for which the output potential ofthe NAND element M remains at the L" level is the other half period. Anoscillating frequency of the oscillator is represented by an equation f=l/T, where T T T The resistor R and the output terminal of the NANDelement M are connected to the trigger terminal T of the counter B Anoutput terminal A of the counter B; is connected to an input terminal Aof the decoder E and in the same way output terminals B and C of thecounter B are connected to input terminals B and C of the encoder Erespectively. In addition, the output C of the counter B is connected toa trigger terminal T of the counter B An output A of the counter B isconnected to an input of NOR element N and output terminals B, C and Dof the counter B are connected to inputs of the NAND element Mrespectively. The output terminal D of the counter B is furtherconnected to an input of the NAND element M in block II.

The output of'the NAND element M is connected to an input of'the NORelement N and an input of-the NAND element M The output of the NORelement N is connected to an input of the NAND element M and the outputof the NAND element M is connected to the input terminal D of theencoder E and to an input of the NAND element M An output terminal 1" ofthe decoder E is connected to an input of the NAND element M and anoutput terminal 3 is setinput-terminals S of the flipflops F to F Anoutput terminal 5 of the encoder E is connected to an input of the NANDelement M and an output terminal 7 is connected to reset-input-terminalsR of the flipflops F to F The composition thus described up to here willbe called block A. Blocks A in blocks II and V can be used in common.

The output of the NAND element M in block II is connected to a triggerinpuf terminal T of the flipflop F and an output terminal Q of theflipflop F is connected to an input of the NAND element M An outputterminal Q of theflipflop F is connected to a trigger input terminal Tof the flipflop F and an output terminal Q of the flipflop F is an inputof the NAND element M An output terminal Q of the flipflop F isconnected to a trigger input terminal T of the flip-flop F and an outputterminal 6 of the flipflop F is connected to an input of the NANDelement M An output terminal Q of the flipflop F is connected to atrigger input terminal T of the flipflop F and an output terminal Q ofthe flipflop F is connected to an input of the NAND element M An outputterminal Q of the flipflop F is connected to a trigger input terminal Tof the flipflop F and an output terminal 6 of the flipflop F isconnected to an input of the NAND element M An output terminal Q of theflipflop F is connected to a trigger input terminal T of the flipflop Fand an output terminal Q of the flipflop F is connected to an inputterminal of the NAND element M The flipflops F to F in combination forma welLknown addition counter. The output of the NAND element M isconnected to inputs of the NAND elements M through M Output terminal ofthe NAND elements M to M are respectively connected toreset-input-terminals of the flipflops F to F The output terminal of theNAND'element M is connected to a trigger input terminal T of theflipflop F and an output terminal Q of the flipflop F is connected to atrigger input terminal T of the flipflop F An output terminal Q of theflipflop F is connected to a trigger input terminal T of the flipflop FAn output terminal Q of the flipflop P is connected to an input terminal D of the flipflop F and an output terminal Q of the flipflop Fis connected to a trigger input terminal T of the flipflop F An outputterminal Q of the flipflop F is connected to an inpu t terminal D of theflipflop F5 and an output terminal Q of the flipflop F is connected to atrigger input terminal T of the flipflop F In the same way, an outputterminal Q of the flipflop F is connected to an input terminal D of theflipflop F and an output terminal Q of the flipflop F is connected to atrigger input terminal T of the flipflop F An output terminal Q of theflipflop F is connected to an input terminal D of the flipflop F Theflipflops F toF in combination constitute a wellknown subtractioncounter.

The output terminal of the NAND element M is connected totrigger-input-terminals T of the flipflops F to F An output terminal Qof the flipflop F is connected to an input termigal of the NAND elementM and an output terminal 0 of the flipflop F is connected to an inputterminal of the NAND element M An output terminal Q of the flipflop F isconnected to an input termina l of the NAND element M and an outputterminal Q of the flipflop F is connected to an input of the NANDelement M An output terminal Q of the flipflop P is connected to aninput terminal of the NAND element M and an output terminal Q of theflipflop F 52 isconnected to an input terminal of the NAND element M Anoutput terminal Q of the flipflop P5 is connected to input terminals ofthe NAND elements M and M and an output terminal Q of the flipflop F isconnected to input terminals of the NAND elements M M and M The outputterminal of the NAND element M is connected to inputs of the NANDelements M and M and the output terminal of the NAND element M isconnected to an input of the NAND element M The output terminal of theNAND element M is connected to an input terminal of the NAND element Mand the output terminal of the NAND element M is connected to inputterminals of the NAND elements M and M The output terminal of the NANDelement M is connected to input terminals of the NAND elements M and Mand the output terminal of the NAND element M is connected to an inputterminal of the NAND element M An trigger input terminal FW of theflipflop F in block II is connected to the previously mentioned outputRT in block IV. A trigger input terminal RW of the flipflop F H (whichis not shown, but the circuit compositions of blocks II and IV aree thesame as stated before) in block V is connected to the previouslymentioned output FT. An input FZ of the NAND element M is connected toone of the outputs RP, RT and R0 of block IV. An input R2 of the NANDelement M in block V is connected to one of the outputs FP, ET and P0 ofblock I. An output terminal Q of the filiptlop P is connected to aninput terminal of the NOR element N an input terminal of the NANDelement M and a trigger input terminal of the flipflop F An outputterminal of the flipflop F is connected to input terminals of the NANDelements M and M and to a trigger input terminal of the flipflop F Anoutput terminal-Q of the flipflop F is connected to input terminals ofthe NAND elements M and M The output terminal of the NAND element M isconnected to an input of the NOR element N and an input terminal of theNAND element M and the output terminal of the NAND element M isconnected to resetinput-terminals R of the flipflops M to M The outputterminal of the NOR element N is connected to a trigger input terminalof the flipflop F The output terminal of the NAND element M. is

connected to a trigger input terminal of the flipflop F g and outputterminal Q of the flipflop F is connected to a trigger input terminal ofthe flipflop F An output terminal Q of the flipflop F is connected to atrigger input terminal of the flipflop F and an output terminal Q of theflipflop F 9 is connected to an input terminal of the NAND element M Anoutput terminal 0 of the flipflop F is connected to an input terminal Dof the flipflop F An outputterminal of the NAND element M is connectedto a trigger input terminal of the flipflop F and an output terminal ofsaid flipflop F iis connected to an input trigger terminal of theflipflop F21.

An output terminal Q of the flipflop F is connected to an input terminalof the NAND element M and a set input terminal S of the flipflop F Anoutput terminal Q of the flipflop P is connected to a'ninput of the NAND element M The output terminal of the NAND element M is connected to aninput of the NAND ele ment M The output terminal of the NAND element Mis connected to a resistor R and the output of the NAND element M is inturn connected to a resistor R2]. 7 I i Said resistors R and R areconnected to bases of transistors T and T respectively, in blocks Illand VI. The emitter terminal of the transistor T, is connected to theelectrical source voltage, and its collector terminal is connected toterminals of resistors R and R The other terminal of the resistor R isconnected to the base of the transistor T The other terminal of theresistor R and the emitter of the transistor T are grounded. Thecollector terminal of the transistor T in block III is connected to oneend of the electromag netic solenoid 22 (FIG. 2) of the actuator 19 usedfor the front wheels. The other end of the solenoid 22 is connected tothe electrical source voltage. The collector terminal of the transistorT (not shown) in block VI is connected to one end of the electromagneticsolenoid 24 (FIG. 2) of the actuator 20 used for the rear wheels. Theother end of the solenoid 24 is connected to the electrical sourcevoltage. The other terminal of the resistor R is connected to the baseof the transistor T the emitter of the transistor T is grounded, and thecollector of the transistor T is connected to resis

1. A digital type brake control system for braking the front and rearwheels of a vehicle which comprises: a master cylinder; wheel cylindersof said wheels; passage means for communicating between said mastercylinder and said wheel cylinders; actuator means provided in saidpassage means, said actuator means including valve means for opening andclosing said passage means and means for varying fluid volumes presentedbetween said valve means and said wheel cylinders; sensor means forsensing the rotational conditions of at least one of said wheels andproviding output signals representative thereof; conversion circuitmeans operating to carry out amplification and waveform-shaping of saidoutput signals from said sensor means and to convert the thus treatedoutput signals into respective wheel pulse signals; control circuitmeans for providing control signals and comprising a clock pulseoscillator, free running counter means and a decoder; addition andsubtraction circuit means comprising addition and subtraction counters,gate circuits and register circuits, said addition and subtractioncircuit means, obtaining, in cooperation with said control signals, adifference between a number of pulses which is obtained by counting saidwheel pulse signals for a predetermined period of time beginning at anoptional time and a number of pulses which is obtained by counting thewheel pulse signals for a predetermined period of time beginning at adifferent optional time; a first comparison circuit means for comparingthe difference in pulse number obtained by said addition and subtractioncircuit means with a first predetermined number of pulses, and forproducing a pressure-reducing signal so as to operate said actuatormeans when the difference in pulse number is greater than said firstpredetermined number of pulses; and a second comparison circuit meansfor comparing the difference in pulse number obtained by the additionand subtraction circuit with a second predetermined number of pulses,and for producing an instruction signal for reducing the rate of varyingthe fluid volume obtained by said actuator means, when the difference inpulse number is smaller than the second predetermined number of pulses.2. A digital type brake control system for braking the front and rearwheels of a vehicle which comprises: a master cylinder; wheel cylindersof said wheels; passage means for communicating between said mastercylinder and said wheel cylinders; actuator means provided in saidpassage means, said actuator means including Valve means for opening andclosing said passage means and means for varying fluid volumes presentedbetween said valve means and the wheel cylinders; sensor means forsensing the rotational conditions of said wheels and providing outputsignals representative thereof; conversion circuit means operating tocarry out the amplification and waveform-shaping of said output signalsfrom said sensor means and to convert the thus treated output signalsinto respective wheel pulse signals. control circuit means for providingcontrol signals and comprising a clock pulse oscillator, free runningcounter means and a decoder; addition and subtraction circuit meanscomprising addition and subtraction counters, gate circuits and registercircuits, said addition and subtraction circuit means obtaining, incooperation with said control signals, a difference between a number ofpulses which is obtained by counting said wheel pulse signalscorresponding to at least one of said wheels for a predetermined periodof time beginning at an optional time and a number of pulses which isobtained by counting the wheel pulse signal for a predetermined periodof time beginning at a different optional time; a first comparisoncircuit means for comparing the difference in pulse number obtained bysaid addition and subtraction circuit means with a predetermined numberof pulses, and for producing a pressure-reducing signal when thedifference in pulse number is greater than said predetermined number ofpulses; a first detection circuit means for detecting the wheel pulsesignal corresponding to that one of said wheels which has the highestrotational speed, and providing a first output signal representativethereof; a second detection circuit means for detecting the wheel pulsesignal corresponding to each of said wheels other than said wheel havingthe highest rotational speed and providing a second output signalrepresentative thereof; a second comparison circuit means for comparingsaid first output signal of said first detection circuit means with saidsecond output signal of said second detection circuit means, said secondcomparison circuit means producing a pressure-reducing signal when theratio of the frequency of the wheel pulse signal of said seconddetection circuit means to that of said first detection circuit issmaller than a predetermined ratio; and a logical circuit means foroperating said actuator means in accordance with a logical addition ofsaid pressure-reducing signal from said first comparison circuit meansand that from said second comparison circuit means.
 3. A digital typecontrol system as claimed in claim 2 wherein said addition andsubtraction circuit means operates with a respective one pair of wheelsfrom among the paired front wheels and rear wheels, said first detectioncircuit means operatively corresponds to the faster of the other pair ofwheels among the paired front wheels and rear wheels; and said seconddetection circuit means operatively corresponds to at least one wheel ofsaid one pair of wheels.
 4. A digital type vehicle brake control systemas claimed in claim 2 which further comprises; circuit means foroperating said actuator means so as to reduce the fluid volume in saidsystem when said difference in pulse number obtained by said additionand subtraction circuit means comes within another predetermined numberof pulses.
 5. A digital type brake control system as claimed in claim 2which further comprises: circuit means for suspending generation of saidpressure-reducing signal in said second comparison circuit means whenthe rotational speed of that wheel having the highest rotational speedis reduced to a predetermined value.
 6. A digital type brake controlsystem as claimed in claim 2 which further comprises; a third comparisoncircuit means for comparing the difference in pulse number obtained bysaid addition and subtraction circuit means with a second predeterminednumber oF pulses, said third comparison circuit means producing aninstruction signal to reduce the rate of varying the fluid volume whichis provided by said actuator means when the difference in pulse numberis smaller than the second predetermined number of pulses.